Coating of pre-cast electrophoresis slab gels

ABSTRACT

In pre-cast slab gel cassettes, the formation of pathways in which proteins can migrate between the gel and the walls of the cassette to form shadow bands is avoided by the application of a coating of a nonionic amphiphilic polymer to the cassette walls. The coating also prevents the gel from sticking to the walls when the gel is to be removed from the cassette after electrophoresis.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is related to and claims the benefit of U.S.provisional patent application No. 60/241,381, filed Oct. 17, 2000, forall legal purposes capable of being served thereby. The contents ofprovisional patent application No. 60/241,381 are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

[0002] This invention relates to polyacrylamide gels as used in slab gelelectrophoresis.

[0003] Slab gels are particularly useful for electrophoresis in view oftheir ability to accommodate multiple sample analyses and the ease withwhich the electropherograms can be observed and read visually byidentifying the locations of the various bands on the gels thatcorrespond to the individual components. Polyacrylamide is a gelmaterial that is widely used in slab gels.

[0004] Slab gels are frequently supplied in pre-cast form, retainedbetween two flat transparent plates in a cassette. The plates may beglass or plastic, a common plastic being a polystyrene-acrylonitrileblend. A difficulty with certain pre-cast polyacrylamide gels is thatthey appear to separate from the cassette plates during storage, leavinga pathway between the gel and one or both of the plates for the sampleto migrate. This apparent pathway is detrimental to the electrophoreticanalysis since the solute bands in the gel tend to migrate into thepathway and spread, forming shadow bands. A shadow band is a band ofprotein that results from the migration of protein away from a parentprotein band during electrophoresis, the parent protein band being thewell-defined band that is formed as a direct result of theelectrophoretic separation. Shadow bands reside mostly on the surface ofthe gel, whereas the parent protein bands extend relatively uniformlythrough the thickness of the gel. The pathways and shadow bands decreasethe shelf life of precast gels and can eventually evolve into a smear ofprotein on the surface of the gel. The shadow bands are a particularproblem in pre-cast gels that have been stored without cooling.

[0005] Another problem encountered with polyacrylamide slab gels is atendency of the gels to stick or adhere to the plates. This presents adifficulty once the separation has been performed and the user attemptsto remove the gel from the plate for purposes of staining, photographingor other observation, detection or recordation. Attempts to remove a gelthat is sticking to one or both of the plates can result in a damagedgel and a ruined experiment. This problem is especially acute for gelsof low concentration and for gels used for isoelectric focusing.

[0006] The polymerization reaction to form polyacrylamide is inhibitedwhen dissolved oxygen is present in the gel-forming liquid at or nearthe gel plate. This is especially true when the gel plates are plastic,such as polystyrene-acrylonitrile, for example. To prevent thisinhibition from occurring, a coating of polyvinylidene chloride orpolyvinyl dichloride (PVDC) is often applied to the plates prior tocontacting the plates with the polyacrylamide gel material.Unfortunately, these coatings produce an effect on the electrophoresisimage that appears to be the result of separation between the gel andthe plate. These coatings also exacerbate the sticking problem when thegel is an isoelectric focusing gel, for example one with a pH rangingfrom 5 to 8.

SUMMARY OF THE INVENTION

[0007] The present invention resides in the discovery that both theoccurrence of what appear to be pathways between a polyacrylamide geland a gel cassette plate and the adherence of the gel to the plate canbe prevented by applying a coating of a nonionic amphiphilic polymer tothe plate surface before the gel is cast. The coating may be applieddirectly to the surface of the glass or plastic plate or it may beapplied over a polyvinylidene chloride or polyvinyl dichloride coatingif such a coating is present. Once the gels are formed over the coating,the gels can be stored for extended periods of time with no extraneouspath formation or sticking problem.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0008] Examples of nonionic amphiphilic polymers that can be used ascoating materials in the practice of this invention are polyvinylalcohol, agarose, polyvinyl pyrrolidone, polyethylene glycol,polypropylene glycol, polypropylene glycol/polyethylene glycolcopolymers, and linear polyacrylamide. Polyvinyl alcohol of 14,000molecular weight (weight-average) for example can be applied as a 1% (byweight) aqueous solution. For polyvinyl alcohol use in general, aweight-average molecular weight ranging from about 10,000 to about100,000 may be applied as an aqueous solution of concentration rangingfrom about 0.5% to saturation. For coatings of polyethylene glycol, anexample is one with a weight-average molecular weight of about 20,000,or a range of from about 10,000 to about 100,000. The polyethyleneglycol can be applied as a 1-4% (by weight) aqueous solution. Theconcentrations and molecular weights of other polymers are readilydetermined by routine experimentation and will in many cases be readilyapparent to those skilled in the art.

[0009] The nonionic amphiphilic polymer solution can be applied by anymeans that will result in a substantially even distribution over theplate surface and a clear film. Examples of application techniques arespin coating, dip coating, and brush coating. Once the film is applied,it can be dried by conventional techniques before it is placed incontact with the gel mixture. Drying can be accomplished by exposure toheat or to air. A particularly convenient drying method is to pass thecoated plate through an infrared tunnel.

[0010] The foregoing description is primarily for purposes ofillustration. Further modifications, substitutions and variations willbe apparent to those skilled in the art and will be included within thescope of the invention.

What is claimed is:
 1. A pre-cast polyacrylamide slab gel for use inslab gel electrophoresis, said pre-cast gel comprising: a pair ofchemically inert, transparent plates with inner surfaces coated with anonionic amphiphilic polymer, and a polyacrylamide gel cast between saidplates.
 2. A pre-cast polyacrylamide slab gel in accordance with claim 1in which said nonionic amphiphilic polymer is polyvinyl alcohol.
 3. Apre-cast polyacrylamide slab gel in accordance with claim 1 in whichsaid nonionic amphiphilic polymer is polyethylene glycol.
 4. A pre-castpolyacrylamide slab gel in accordance with claim 1 in which said platesare glass.
 5. A pre-cast polyacrylamide slab gel in accordance withclaim 1 in which said plates are plastic.
 6. A pre-cast polyacrylamideslab gel in accordance with claim 1 in which said plates arepolystyrene-acrylonitrile blend.
 7. A pre-cast polyacrylamide slab gelin accordance with claim 1 further comprising a coating ofpolyvinylidene chloride between said plate and said coating of nonionicamphiphilic polymer.